Django save（）方法中应为string或byteslike对象

Question

我有Job Model，我可以看到它们的列表，创建一个新的，并查看其中一个的详细信息。但是当我想编辑这个模型的对象时，我得到了一个错误：

match = datetime_re.match(value)
TypeError: expected string or bytes-like object

在Traceback中，这一行用粗体表示：

job_resume.save()

这是我的文件：

#Views.py
resume = get_object_or_404(JobRecord, id=id)
if request.method == "POST":
    form = AddAdminJobForm(request.POST,  request.FILES,instance=resume)
    if form.is_valid():
        job_resume = form.save(commit=False)
        job_resume.upload_url = form.cleaned_data['upload_url']
        job_resume.time_start = date_picker(date=request.POST['time-start-input'])
        job_resume.time_end = date_picker(date=request.POST['time-end-input'])
        job_resume.save()
        return redirect('administrator:view_admin_job_resume')
else:
    form = AddAdminJobForm(instance=resume)
template = 'administrator/resumes/add_edit_resume.html'
context = {'form': form}
return render(request, template, context)

#forms.py 
class AddAdminJobForm(ModelForm):
class Meta:
    model = JobRecord
    fields = '__all__'

#date_picker function:
def date_picker(date):
if date:
    gregorian_date = jdatetime.date.togregorian(jdatetime.datetime.strptime(date, "%Y/%m/%d"))
else:
    gregorian_date  = jdatetime.date.togregorian(jdatetime.datetime.now().date())
return gregorian_date

这个代码有什么问题？